Mobile terminals such as mobile phones, personal digital assistants (PDAs) and the like, are driven by rechargeable batteries due to their nature, and the battery of such mobile terminals is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by foreign substances. As a result, battery charging is not correctly performed. Further, the battery charging may not be correctly performed when the contact terminal is exposed to moisture.
Recently, a wireless charging or non-contact charging technology has been developed and used for electronic devices to solve the above-mentioned problems.
The wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged if the battery is simply placed on a charging pad, without connecting the mobile phone to a separate charging connector. Such wireless charging technology is generally known to people through association with wireless electrical toothbrushes or wireless electric shavers. The wireless charging technology can improve a waterproofing function because it can be used to wirelessly charge the electronic devices. The wireless charging technology can also improve the portability of the electronic devices because it does not require a wired charger. Therefore, it is expected that technologies related to wireless charging will significantly develop in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and a radio frequency (RF)/microwave radiation scheme converting electrical energy to microwave radiation, and then transmitting the microwave radiation.
Currently, the electromagnetic induction scheme is considered the mainstream technology, but it is expected that soon all electronic products will be wirelessly charged, anytime and anywhere, without a wire through the use of microwaves at home and abroad, based on the strength of recent successful experiments for wirelessly transmitting power to destinations separated by dozens of meters.
A power transmission method through electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnetic is moved in a coil, an induction current occurs. By using the induction current, a magnetic field is generated at a transmitting end, and an electric current is induced according to a change in the magnetic field so as to generate energy at a receiving end. The phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has a high energy transmission efficiency.
With respect to the resonance scheme, in 2005, Prof. Soljacic of The Massachusetts Institute of Technology (MIT) announced a system in which electricity is wirelessly transferred using an electric power transmission principle of resonance based on a coupled mode theory, even if a device to be charged is separated from a charging device by several meters. The MIT research team made an electromagnetic wave containing electrical energy resonating instead of making sounds resonating. It is known that resonant electrical energy does not affect surrounding machines or human bodies, differently from other electromagnetic waves, because the resonant electrical energy is directly transferred only to a device having a resonance frequency and unused parts are reabsorbed into an electromagnetic field instead of spreading into the air.
In order to make a television (TV), monitor, or home appliance wireless by removing a power line therefrom, a battery and wireless power transmission may be considered. Although battery technology has been improved, battery life may still be limited by the number of times by which the battery is charged and discharged. Therefore, a need exists to provide power through wireless power transmission without the aid of a battery.
The wireless power transmission of the related art is still based on a battery environment in which a load is determined by a charging current of a battery, and is controlled based on the charging current of a battery. However, since the wireless power transmission has a wider load change range and varies within a short time compared to the load by the charging current of a battery, it is difficult to perform the wireless power transmission through the schemes of the related art.
The above information is presented as background information only, and to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.